Retinol (Vitamin A) is known to be necessary to the biochemistry of human vision. Through a series of reactions, the retinol is converted through retinal isomers to rhodopsin ("visual purple"). Irradiation of the rhodopsin with visible light in turn causes a series of isomerization reactions through the retinal isomers to opsin resulting in excitation of the retinal rod cells and generation of a visual nerve impulse. A deficiency of Vitamin A in the system leads to reduced visual sensitivity (especially night blindness) and in extreme cases (e.g., keratomalacia or xerophthalmia) to complete blindness.
Vitamin A is also known to be necessary to the proper function of the epithelial tissues. Deficiency of Vitamin A in such cases results in disorders such as reduced resistance to infection through epithelial surfaces.
Increases of level of Vitamin A in the body may to some extent be obtained by administering doses of Vitamin A directly to an individual. However, there is a limited bodily tolerance to Vitamin A, and overdoses of Vitamin A can lead to toxic effects. Since the tolerance level varies widely among individuals, it is not generally advisable to administer substantial doses of Vitamin A except under carefully controlled circumstances.
It is well known that carotene is the precursor of Vitamin A. (There are several carotene isomers, including the alpha-, beta- and gamma- isomers. Of these the beta- isomer is the most active for Vitamin A activity and is also the most common. As used herein, the terms "carotene" or "the carotenes" will refer to mixtures of two or more of the isomers or to an individual isomer as appropriate to the context. If a particular isomer is of specific importance in a given context, it will be so identified.) The carotenes are oxidized by liver enzymes to produce Vitamin A. Significantly, however, the enzyme metabolism produces only the amount of Vitamin A that can be utilized by the body; it cannot produce an overdose of Vitamin A. Consequently, an individual can be administered doses of carotene in quantities large enough to produce optimum levels of Vitamin A in the body without the risk of a toxic Vitamin A reaction. Excess carotene which is administered is stored in fatty tissues and organs.
The carotenes, particularly beta-carotene, are present in many common foods, primarily the green and yellow vegetables such as tomatoes, citrus fruits, carrots, squash, turnips, broccoli and spinach. The concentration of carotene in these vegetables is relatively low, and a person must consume substantial quantites of the vegetables to have a high intake level of carotene. The normal diet of most people does not include such large quantities of these types of vegetables, so there has developed a commercial market for concentrated carotene dietary supplements, particularly those in which the carotene is beta-cartoene because of its high Vitamin A activity. These supplements normally have been produced by extraction of carotene from vegetables such as carrots by use of petrochemical solvents. The resulting carotene, usually in crystalline form, can be expected to be associated with at least residual quantities of such solvents. This is particularly true when the carotene is administered in a dosage form in which it is dispersed in a petrochemical or other "synthetic" oil. The presence of such petrochemical residues in the carotene supplements, even in minute amounts, has caused apprehension among users of the supplements.
It is also known that certain algae, especially those in the classes Rhodophyta (red algae) and Chlorophyta (green algae), are good sources of carotene. The carotene content of species of the genus Dunaliella have been reported in U.S. Pat. Nos. 4,115,949 and 4,119,895 and in Acta Chem. Scand., 23, 7, 2544-2545 (1979). Similar data for the genus Chlorococcum are disclosed in U.S. Pat. No. 2,949,700. In the past, however, extraction processes to produce the carotene from algae have involved the use of petrochemical solvents, which produces the same residual contamination problems discussed above for the vegetable extractions. In addition, many of the algal extraction processes have involved drying of the alga, which has been found to reduce the yield of carotene which may be recovered from the alga. Typical of such extraction processes are those described in the aforesaid U.S. Pat. Nos. 4,155,949 and 4,199,895, which use solvents such as hexane and cyclohexane.
In addition to the use of carotene as a precursor for Vitamin A, there have recently been reports in the literature that suggest that carotene is itself useful in the prevention of certain types of cancers which are believed to be promoted by oxidizing free radicals. It is postulated that carotene, which has an affinity for such free radicals, may serve to reduce the free radical level in the body, thereby reducing the occurrence of free radical initiation of malignancies. There are studies currently underway which are expected to provide more information regarding the effects of carotene on such cancers.
The carotenes can also be used in supplementation of poultry and livestock feeds.
It would therefore be of benefit to have a process available which would yield commercial quantities of carotene in a form which would be safe and therapeutically useful for humans, and which would not result in petrochemical contamination of the carotene. It would also be advantageous for such a process to be capable of extracting and recovering virtually all of the available carotene from algae without the significant losses encountered in the prior art processes which involve thorough drying of the algae.